Robert L. Brown

Effects of N‐Atom Concentration, Pressure, and Carrier Composition on Some First Positive Band Intensities in the Yellow Nitrogen Afterglow

Absolute intensities of seven N2 1st positive bands with υ′ = 6–12 were measured as a function of carrier pressure, carrier composition, and N‐atom concentration in the range 4.5–0.06 torr. For an Ar carrier large pressure‐dependent shifts in the B 3Πg vibrational distribution to higher levels were observed below 4 torr; similar but much smaller shifts were also found for N2 and He carriers. With Ar, reducing the N‐atom concentration shifted the vibrational distribution to lower levels. Changes in carrier composition produced large pressure dependent changes in the absolute and relative band intensities. An attempt was made to fit the results to a model involving vibrational relaxation and electronic quenching in B 3Π. While qualitatively successful, this model could not account quantitatively for the observed relative intensity changes over the whole pressure range for which data are available and, in addition, implied physically unreasonable vibrational relaxation rates. It is suggested that the observe...

Isotopic Determination of the Vibrational Numbering for the B3Π0+u State of Iodine

A measurement of the vibrational isotope displacements between 127I2 and 129I2 has confirmed the revised vibrational numbering of the B3Π0+u state proposed by Steinfeld et al. They have observed that the traditional numbering must be decreased by one unit to bring their calculated fluorescence intensity distributions into agreement with experiment.

Spin‐Relaxation Effects on the EPR Spectrum of Gaseous Nitrogen Atoms

Experimental evidence is presented which indicates that N atoms produced in a flow system by a microwave discharge through purified N2 can have a relaxation time T1 comparable to their residence time in the EPR magnetic field. As a result, atoms generated outside the field (and therefore unmagnetized) can arrive at the microwave cavity before reaching their equilibrium magnetization. Under such conditions, we found that addition to the discharged N2 of as little as 40‐ppm O2 (which did not affect the N‐atom concentration) decreased T1 and led to increases as great as sevenfold in unsaturated N‐atom EPR line intensities. Interpreting the effects of O2 addition in terms of a two‐level spin model for N, we estimated a value of ≃0.5×10−15 cm2 for the N–O2 spin‐exchange cross section. Without added O2, power saturation of the N‐atom lines was found to be governed primarily by the rate at which unsaturated atoms entered the cavity and not by collision relaxation processes. Several qualitative observations regar...

Relative thermochemical stabilities and reactivities of benzo[a]pyrene and selected isomers

Abstract Gas-phase standard enthalpies of formation are calculated for benzo[ a ]pyrene and thirty-two isomeric polycyclic aromatic hydrocarbons including compounds having four-five- and seven-membered rings. Additionally, reactivity data are summarized and include experimental ionization potentials, Huckel highest occupied molecular orbitals and selected reactivity indices. These data are compared with levels of those C 20 H 12 hydrocarbons reported in the atmosphere. These thermodynamic and kinetic parameters are useful reference points for understanding the stabilities of airborne PAH. Additionally, the data tabulations may be useful in predicting the existence of PAH not yet reported in environmental samples.

Partition coefficients and solubility measurements of dimethylmercury in fresh and sea water over a temperature range 0–25°C

Abstract The partition coefficients and solubilities of dimethylmercury in distilled and sea water over a temperature range 0–25°C, have been measured using a head‐space technique.

Determination of Hydrocarbon Solubility in Sea Water and the Analysis of Hydrocarbons in Water-Extracts

ABSTRACT An apparatus is described for measuring the solubility of hydrocarbons in sea water and for analyzing hydrocarbons in water-extracts. The relative concentrations of the hydrocarbons in the gas phase in equilibrium with the water extract were determined by gas chromatography. A known volume of the gas phase was purged out from the apparatus and replaced with helium. The concentration of the hydrocarbons were measured after the second equilibration. The solubility of the hydrocarbon solutes in the sea water extract were determined from the peak area ratios of the solute peaks and the volume of the apparatus. Complex mixtures of hydrocarbons in aqueous solutions may be analyzed using this apparatus by examining the chromatograms obtained after each flush out. The peaks are identified as to hydrocarbon group (olefinic, aromatic, paraffinic) from the rate that the solute peak area decreases after each flush out. Overlapping peaks may be resolved using this technique. By extrapolating peak areas to zer...

Line parameters of absorption and dispersion Lorentzian curves under conditions of combined modulation and saturation distortion

Analytical and computer solutions for the parameters of the first Fourier coefficients of Lorentzian lines subject to simultaneous modulation and saturation distortion are presented. Both absorption and dispersion shape functions are examined. The system is assumed to be described by the saturation theory of either Bloembergen, Purcell, and Pound (BPP), or Redfield. In the BPP case, results are given for the modulation frequency, ωm, being much greater or less than 1T1 while in the Redfield case, only ωm ⪡ 1T1 is considered. In all cases, it is assumed that ωm2π is much less than the inverse line width of the pure absorption curve and that the line is traversed during a time which is slow compared to T1 and 2πωm. Various methods are outlined for determining the true line width, line intensity, saturation parameter, and modulation amplitude from measurements on the distorted line shapes under conditions of optimum sensitivity. Tests for verifying the character of the Lorentzian line shape are also suggested.

Modeling of axially symmetric flow reactors

Abstract A method of calculating the velocity profiles and species concentrations in axially symmetric flow reactors is presented. The method is illustrated with a reactor consisting of three concentric tubes arranged so that reactants flow through the inner tube and inner annulus to a mixing region and the products flow out through the outer annulus. A single bimolecular reaction is used in the example. The method involves two steps; calculation of the velocity field from a solution of the Navier-Stokes equations, followed by solution of the species conservation equations. The technique provides a way of analyzing reactors with variable cross sections and sampling ports near mixing regions.

Use of Fiber Optics in the Study of Chemiluminescent Reactions

The use of stationary light pipes and a stationary detector to measure light decay along a tube in a steady state flow system is described. This method exhibits a number of advantages over that of moving the detector. A means of calibrating the transmission of the light pipes in situ by using the properties of the yellow nitrogen afterglow is discussed. The high degree of spatial resolution achievable by this technique should make it especially suitable for studies of small flames and discharges.